Malaria is the most devastating parasitic disease affecting humans. Each year, there are 350-500 million clinical cases and greater than one million deaths due to malaria, primarily of children in sub-Saharan Africa. There is an urgent need for a safe and effective malaria vaccine and the development of such a vaccine is a global health priority. Adenovirus type 5 (Ad5) based vectors are capable of generating robust and protective T cell and antibody responses in animal models for malaria and other infectious diseases. Ad5 vectors have induced potent CD4+ and CD8+ T cell and antibody responses in clinical trials for HIV, and are currently being evaluated as a vaccine for malaria. However, the high prevalence of neutralizing antibodies (NAB) to Ad5 in human populations, especially in sub-Saharan Africa, has the potential to limit the effectiveness of an Ad5- based malaria vaccine. These Ad5-specific NAB recognize determinants in the hypervariable regions (HVR) of the hexon and on the fiber protein of the Ad5 virion. We hypothesize that modification of the determinants of neutralizing antibodies on the Ad5 virion will enhance vaccine-induced immunity by circumventing Ad5 NAB responses. We propose to develop a capsid-modified Ad5 malaria vaccine that will induce robust antigen specific-T cell and antibody responses and is not limited by pre-existing Ad5 NAB. We will utilize an optimized pre-erythrocytic stage malaria antigen, PfCSP(-GPI), as the PfCSP antigen is a major target of protective immune responses in humans. We will generate adenovectors that have modifications in the Ad5 hexon HVR, and additional vectors with modifications both the hexon HVR and the fiber knob. These vectors will be evaluated for growth, avoidance of NAB from human sera obtained from volunteers in the US and Africa, and immunogenicity in mice pre-immunized with Ad5 vectors to generate pre-existing Ad5 NAB. In addition, we will evaluate these vectors in heterologous adenovector prime-boost regimens. Our goal is to advance a capsid- modified Ad5-based malaria vaccine that induces potent immune responses in the presence of Ad5 NAB to clinical testing in Phase 2 of this SBIR. If successful, these studies will lead to the development of an effective malaria vaccine and the capsid modification technology could be applied to adenovector vaccines for other infectious diseases and vector delivered therapeutics.